Recently, functions of metal complexes such as photoreactive functions, electron-transfer functions, and physiologically active functions have been attracting attention, and a number of researches are being conducted by utilizing such functions. Further, researches on ligands that bind to metal elements have also been conducted. As a representative ligand, a unidentate ligand such as ammonia, pyridine, and a cyanide ion, a bidentate ligand such as ethylenediamine, bipyridine, and glycinato, and a multidentate ligand having a coordination number of three or more such as ethylenediaminete-traacetic acid are known.
Bipyridine, which is a representative bidentate ligand, has a chelate ligand structure and a function of coordinating with a metal element. However, owing to poor solubility of bipyridine metal complexes in organic solvents, there has been a problem that the utility range of such a complex is extremely limited.
Patent Literature 1 discloses a compound in which a long chain alkyl group such as a hexyl group, pentyl group, octyl group or decyl group is introduced into a polypyridine.
Although Patent Literature 2 discloses a phenanthroline compound in which an aromatic cyclic group has been substituted, there is no description of a metal complex having the phenanthroline compound as a ligand thereof. Examples of ligands of the metal complex described in this document include phenylpyridine, quinoline and benzimidazole, and these compounds have completely different structures from the ligands of the rare earth metal complexes of the present invention.
Non-Patent Literature 1 discloses a ligand that is a 2-pyridylphenanthroline compound, and describes a ruthenium complex having this ligand. In addition, although Non-Patent Literature 2 discloses phenanthroline compounds having a 2-pyridyl group or phenyl group, the structures of both of these compounds are completely different from the ligands of the rare earth metal complexes of the present invention.